Arc processing systems include welders and plasma cutters that generate and apply electrical arcs to workpieces in welding or cutting operations. Welders typically include various subsystems and components, such as power sources, motorized wire feeders, shielding gas supplies, etc., which operate in a coordinated fashion to perform a welding operation. During operation, one or more subsystems may experience fault conditions that cause unexpected failure or shutdown of the subsystem. For instance, welding power sources heat up during normal use, particularly during extended operation at high current levels (e.g., high duty cycle operation of switching power supplies for long periods of time). Switching power supplies in particular include power transistors which are prone to overheating, wherein exceeding the thermal budget of welding power sources or electrical components thereof may cause component degradation and/or failure, as well as unexpected shutdown of the power source. Other examples of arc processing system fault conditions include overheated motor windings, short circuit conditions, reduced supply of process shielding gases, reduced coolant performance for fluid cooled torches, or exhaustion of a supply of consumable welding wire.
These conditions are particularly problematic when a subsystem failure or shutdown causes premature termination of a welding or other arc processing operation. For instance, an abrupt shutdown of a welder operating on workpieces traveling along a production line may require stoppage of the line and removal of a workpiece for scrap or rework. In addition, the line may need to be stopped for an extended time to repair or restart the welder once the fault condition has been removed. Even where such fault situations do not lead to catastrophic component failure, these conditions may degrade a subsystem or component of the arc processing system, thereby adversely affecting welder operation and/or reducing the quality of the finished workpieces. Fault conditions in one subsystem, moreover, may adversely affect another subsystem. For example, a welding torch may be damaged if a welding wire supply is exhausted during a welding operation and the power source does not discontinue the output voltage, resulting in damage to the contact tip of the welding torch and possibly failure or rejection of the welded workpiece. In another example, degradation or failure of fluid-cooled welding torches may occur if the cooling water flow is too low and/or if the coolant temperature is too high.
In order to minimize damage to system components and corruption of welding or cutting operations, conventional arc processing systems often employ one or more sensors or monitoring systems to ascertain the operational condition of system components and/or subsystems. Examples include systems for monitoring welding wire supply levels as presented in Daniel, pending U.S. patent application Ser. No. 10/954,945, filed Sep. 30, 2004, entitled MONITORING DEVICE FOR WELDING WIRE SUPPLY, which is not prior art, the entirety of which is hereby incorporated by reference as background information. When a fault condition is indicated, the system shuts down and may indicate the type of error. In this regard, welding power sources may include thermal sensors such as RTDs, thermocouples, etc. to ascertain the temperature of power switching devices, wherein a system fault may be triggered by a thermocouple signal transitioning above a predetermined value. Samodell U.S. Pat. No. 6,570,129 discloses a protection device for a dual stage power source, and is incorporated by reference as background information. System shutdown may involve the power source stopping current flow and thereby extinguishing the welding arc, after which the operator must wait until the power source cools sufficiently to restart the system. If the welder includes a display, a status message may be provided telling the operator the nature of the fault.
Although this technique can be used to successfully avoid thermal failure of the power source switching components, immediate system shutdown is undesirable because the operator does not know in advance that a fault will occur, and the shutdown may happen in the middle of a weld operation. In this instance, the weld joint being created during the shutdown may be deficient and require repair or rework, or the immediate shutdown may render a workpiece unusable. For example, the fault/shutdown could occur at a critical point of the weld, or a finishing sequence of a multi-step welding operation could be missed, such as a crater fill. In systems without operator displays, an unexpected shutdown could lead the operator to conclude that something is broken, or that the supply voltage to the welder has been discontinued, or the operator may make other false assumptions regarding the cause of the system stoppage. Accordingly, there is a need for improved systems and techniques by which components of arc processing systems can be protected against overload damage and process quality can be maintained, while avoiding system down time and workpiece scrap or rework caused by uncontrolled and/or unanticipated system shutdown.